Embryonic antigens obtained from chemical and virus induced tumors will be identified and characterized. Purification procedures will consist of rate zonal density gradient, PAGE, and isoelectric focusing techniques. Monospecific antisera will be raised to the embryonic components and specificities will be confirmed by immunoelectrophoresis. Preliminary evaluations of select physical/chemical characteristics will be obtained using PAGE in SDS gels, other electrophoresis techniques, and isoelectric focusing. Biological characterization of the embryonic antigens will proceed from identification of their sites of production (using FAB tests) in the syngeneic embryo to elucidation of the role of these antigens in growing tumors and other malignant cells. In vitro tissue culture systems will enable controlled experiments to study the relationship between viral infection and embryonic antigen synthesis. Immunological studies will follow with determinations of the antigenicity of embryonic components regarding their ability: (1) to protect against tumor growth in sensitized animals (i.e. embryonic antigen immunizations); (2) to elicit blocking antibodies (microcytotoxicity tests) which interfere with host-mediated tumor cell destruction; and (3) to determine if the presence of embryonic antigens on the surface of transformed cells (colony inhibition tests) interferes with cell-mediated destruction of target cells. Finally, mechanisms of embryonic antigen production will be studied by non-specifically stimulating antigen production using IUDR or BUDR. Intracellular viral/embryonic antigen modulation by neuraminadase will be used to differentiate between new synthesis and "unmasking" processes in transformed cells. Quantitative estimates of soluble and insoluble embryonic antigen will be made in transformed cells and compared at various stages of tumor growth.